PROJECT SUMMARY/ABSTRACT In the U.S., nearly 500,000 patients suffer an ST-elevation myocardial infarction (STEMI) each year, the majority of which initially present to emergency departments (EDs). More than 60% of U.S. hospitals do not have have the capabilities to perform the primary percutaneous coronary intervention (PCI), the preferred strategy for myocardial reperfusion. Thus, patients must be transferred to capable facilities which are associated with delays for nearly 90% of patients and worse patient outcomes. Our research team has identified that insurance status is a key non-medical predictor of increased transfer. Patients with STEMI who lack insurance presenting to the ED were 60% more likely to be transferred compared with patients with any form of insurance. Two potential reasons for this finding include uninsured patients presenting to facilities without PCI capabilities and alternatively, uninsured patients being transferred unnecessarily from facilities that have PCI capabilities. The objective of this study is to identify the underlying mechanism resulting in disproportionately higher inter- facility transfer rates for uninsured patients with STEMI. Whether the uninsured have diminished access to PCI-capable facilities, or they are transferred from PCI-capable facilities, either explanation has important policy implications for reducing this disparity in access to optimal management of this time-sensitive emergency medical condition. We have identified an established dataset, the Office of Statewide Health Planning and Development (OSHPD) dataset in California which has detailed ED visit data which will allow us identify the underlying mechanism of higher transfer rates. Combined with important health policy changes broadening health insurance access including the early expansion of Medi-Cal at the county-level, this provides an important natural experiment to understand how insurance access affects access to care for time- sensitive emergencies like STEMI. This proposal describes an analysis of the existing datasets to understand the mechanism of more patients with STEMI who lack insurance and are transferred at a much higher rate. The Specific Aims are: 1) Describe the incidence, longitudinal trends, and transfer status of patients with STEMI presenting to California EDs by facility PCI capability; 2) Use Medicaid expansion in California to estimate the relationship between insurance status and transfer of patients presenting to California EDs with STEMI, and assess whether PCI capability modifies these relationships. We have assembled a multidisciplinary team of experts in cardiology, emergency medicine, health policy, health services research, biostatistics, epidemiology, and systems science. We anticipate that the knowledge gained from this will inform policy makers seeking to understand disparities in care, and to understand whether insurance expansion is a potential intervention to address these disparities.